Two fair dice are thrown. What is the probability that the absolute difference between the two numbers is 2 or 3?
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A7/18
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B3/11
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C5/18
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D1/2
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ENone of these
Answer
Correct Answer: 7/18
Explanation
Introduction / Context:We count ordered pairs (a,b) with a,b ∈ {1,…,6} such that |a − b| ∈ {2,3}. Counting favorable outcomes directly is efficient for small dice problems.
Given Data / Assumptions:
- Sample space size = 36 equally likely ordered pairs.
- We need |a − b| = 2 or 3.
Concept / Approach:Enumerate the pairs for |a − b| = 2 and for |a − b| = 3. Sum them, divide by 36.
Step-by-Step Solution:
|a − b| = 2 pairs: (1,3),(3,1),(2,4),(4,2),(3,5),(5,3),(4,6),(6,4) ⇒ 8.|a − b| = 3 pairs: (1,4),(4,1),(2,5),(5,2),(3,6),(6,3) ⇒ 6.Total favorable = 8 + 6 = 14; probability = 14/36 = 7/18.Verification / Alternative check:Symmetry around the main diagonal implies for each a there are at most two b values satisfying |a − b| = k; tabulation matches the counts above.
Why Other Options Are Wrong:5/18 corresponds to only one of the difference values; 1/2 greatly overestimates the event; 3/11 is not tied to a 36-sized space.
Common Pitfalls:Forgetting that outcomes are ordered, or double-counting/omitting symmetric pairs.
Final Answer:7/18